GB2313687A - Semiconductor memory including a peripheral circuit and voltage boosting circuits - Google Patents

Abstract

A semiconductor memory comprises a peripheral circuit comprising a MOS transistor 40, a first boosting circuit (Fig 1) for boosting a power supply voltage to provide a first boosted power supply voltage VPP at a first level to a bulk bias terminal 44 of the transistor, and a second boosting circuit (Fig 4) for boosting the power supply to provide a second boosted voltage AVPP at a second level to the source terminal of the transistor when an external input control signal is activated. Circuit details of the first and second voltage boosting circuits are described (Figs 1 and 4). The peripheral circuit is a word line driver.

Description

VOLTAGE BOOSTING CIRCUITS The present invention relates to boosting circuits for semiconductor memory devices and to memory devices having such boosting circuits.

As semiconductor memory devices become more advanced in their density, their operating voltages go ever lower. The chip operating voltage represents the power supply voltage to be applied to a transistor within the chip so that switching operation of the transistor is performed.

For example, in the case of a 4 mega dynamic RAM, the operating voltage is maintained at 5 volts, but in the case of a 16 mega dynamic RAM intended to employ an internal power supply voltage generator, the operating voltage is maintained at about 4 volts. Further, in the case of a 64 mega dynamic RAM, the operating voltage is lowered to about 3.3 volts. Accordingly, with such a lower operating voltage, the problem arises that it is impossible to operate the chip at high speed. Therefore, in order to solve this problem it is proposed to include a boosting circuit in the high-density semiconductor memory device, the boosting circuit being used for boosting the operating voltage to a predetermined level.

The boosting circuit generates a boosted power supply voltage VPP having a higher level than the operating voltage applied from outside the chip. The boosted power supply voltage VPP is used in the word line driver and the data output buffer of a high-density dynamic RAM. The word line driver enables the word line to a level of the boosted power supply voltage VPP and the data output buffer uses the boosted power supply voltage VPP to prevent data corruption due to a voltage drop during its transmission to its destination. In order to sense data of the memory cell in a bit line sense amplifier having an NMOS sense amplifier and a PMOS sense amplifier, the boosted power supply voltage VPP is provided to a control electrode of an N-type isolation transistor whose channel is connected to the bit line so that two adjacent memory cell arrays can share the bit line sense amplifier. Thus, the bit line sensing margin caused by the threshold voltage of the isolation transistor is reduced, in case that power supply voltage Vcc is typically provided to the control electrode of the insolation transistor.

The above boosting circuit according to the prior art comprises an oscillator 12, a booster 14, a transferrer 16, and a detector 18.

Fig. 2 is a timing diagram of the boosting circuit of Fig.

1. Referring to Fig. 2, the operation of the boosting circuit of Fig. 1 according to prior art will now be explained.

As shown in Fig. 2, if the power supply voltage Vcc is applied to the interior of the chip, the oscillator 12 of Fig. 1 provides an oscillated clock to an input terminal of an inverter 20 of the booster 14. At this time, the output level of the oscillated signal output from the oscillator 12 is the same as the level of the power supply voltage Vcc.

Accordingly, when the output level of the oscillator 12 is the level of a ground voltage Vss, the level of a connection node N1 of a MOS capacitor connected to an output terminal of an inverter 22 which is serially connected to the inverter 20, goes to "On volt, as shown in Fig. 2. At this moment, the voltage level of a connection node N2 within the booster 14 is pre-charged to the level of "Vcc-V*" obtained by subtracting the threshold voltage V of the transistor 26 from the power supply voltage Vcc.

If the level of the oscillating signal output from the oscillator 12 is changed to the level of the power supply voltage Vcc from "0" volts, the connection node N1 of the booster 14 is raised to the level of the power supply voltage Vcc from "0" volts. At this moment, the voltage of the connection node N2 between the capacitor 24 of the booster 14 and the transistor 26 is boosted to the level of "2Vcc-V*" from the level of "Vcc-V*" precharged by the power supply voltage Vcc output from the inverter 22. The boosted power supply voltage of the connection node N2 to the level of n 2Vcc-V* is transmitted to the aforementioned circuit through a transmission transistor 28. Accordingly, the level of the boosted power supply voltage, as shown in Fig.

2, is boosted to a voltage having the level of 2(Vcc-V*) from a level of V -V through the above continuous operation.

As shown in Fig. 2, if the oscillator 12 of Fig. 1 performs consecutive oscillation operations, the level of the boosted power supply voltage VPP is continuously raised as shown in Fig. 2. The level of the boosted power supply voltage VPP is sensed by the detector 18 connected between the oscillator 12 and the boosted power supply voltage VPP.

The detector 18 detects the voltage level when the boosted power supply voltage VPP exceeds the preset reference level, and then generates a signal for disabling the operation of the oscillator 12. Thus, if the boosted power supply voltage VPP is higher than the preset reference level, the operation of the oscillator 12 is stopped by the disable signal output from the detector 18 and the level of the boosted power supply voltage VPP is lowered.

The boosted power supply voltage VPP generated according to the configuration of Fig. 1 is provided to the word line driver, the data output buffer, or a control voltage electrode of the isolation transistor.

Fig. 3 is a diagram illustrating the word line driver for driving a word line selection signal output from a row decoder 30. The word line driver is operated by the boosted power supply voltage VPP generated from the boosting circuit of Fig. 1. The boosted power supply voltage VPP is provided to the sources of first to third PMOS transistors 34, 38, and 40, and a backbias terminal, i.e., a bulk bias terminal 44. A drain of the first PMOS transistor 34 is connected to that of a first NMOS transistor 36 through an internal node 46. The gates of the first PMOS transistor 34 and the first NMOS transistor 36 are commonly connected to an output terminal of the row decoder 30.

In addition, a drain of the third PMOS transistor 40 is coupled to that of the second NMOS transistor 42 through an output node 48 and gates of the third PMOS transistor 40 and the second NMOS transistor 42 are commonly connected to the internal node 46. A source and a drain of the second PMOS transistor 38 are connected to the boosted power supply voltage VPP and the internal node 46, respectively, and its gate is coupled to the output node 48. Therefore, it can be seen that one structure consisting of the first PMOS transistor 34 and the first NMOS transistor 36, and another structure consisting of the third PMOS transistor 40 and the second NMOS transistor 42 are inverter structures. The first to third PMOS transistors 34, 38, and 40 have their sources and drains arranged within an N-type well formed on a P-type substrate.

In the above word line driver, if the word line selection signal at the active state, for example, the logic "high" level, is output from the row decoder 30, the signal is provided to the gates of the first PMOS transistor 34 and the first NMOS transistor 36, respectively. At that point, the level of the word line selection signal output from the row decoder 30 is the same as that of the internal power supply voltage. That is, the level is lower than the boosted power supply voltage VPP. The first PMOS transistor 34 and the first NMOS transistor 36 are turned off and turned on, respectively, by the word line selection signal input to their gates. Hence, the potential of the internal node 46 goes to the "low" level. And, when the potential of the internal node 46 is at the "low" level, the third PMOS transistor 40 and the second NMOS transistor 42 receive the potential at their gate, and are turned on and off respectively. Accordingly, the output node 48 is raised in its level to the boosted voltage VPP to be applied to the source of the third PMOS transistor 40, and the signal of the boosted power supply voltage VPP at the logic "high" level enables the word line WL.

The second PMOS transistor 38 whose source and drain are coupled between the boosted power supply voltage VPP and the internal node 46 is turned on when the level of the output node 48 is at the logic "low" level, and thus charges the internal node 46 to the boosted power supply voltage VPP. Moreover, the second PMOS transistor 38 provides the boosted power supply voltage VPP to the gate of the second NMOS transistor 42. Thus, the time required in inactivating the output node 48 is reduced.

In the semiconductor memory device chips, there are many PMOS transistors to be operated by the boosted power supply voltage VPP output from the boosting circuit of Fig. 1.

The many PMOS transistors within the chip receive the boosted power supply voltage VPP as source voltages. Row decoder configurated from PMOS transistor are commonly used and the boosted power supply voltage VPP used in such row decoders should be provided from a boosting circuit such as Fig. 1. However, if the boosted power supply voltage VPP generated from the boosting circuit having the configuration of Fig. 1 is provided to the bulk bias terminal and the source terminal of the PMOS transistor of the circuit constructed according to Fig. 3, many problems may arise as follows.

Firstly, the capacity of an N-type well capacitor becomes very large, the N-type well capacitor being connected, in a bulk bias, with a PN junction of the source terminal of the PMOS transistor connected to the boosted power supply voltage VPP. Thus, when the boosted power supply voltage VPP is provided from the boosting circuit of Fig. 1, the output of the booster 14 cannot arrive at the desired level of the boosted power supply voltage VPP in just one oscillator cycle, as shown in the timing diagram of Fig. 2, because the large capacitance must be driven. Therefore, only when several tens of oscillator cycles are undergone can the output arrive at the desired level. This means that much time is required in boosting the power supply voltage Vcc to the desired level. Thus, it is difficult to perform high speed operations of the semiconductor memory device.

Secondly, when the semiconductor memory device is in the standby mode, if there are many nodes which should be precharged to the level of the boosted power supply voltage VPP, problems may arise. That is, if there is a bridge between a voltage node (or line) and the ground voltage V, using the boosted power supply voltage VPP and the node (or line) pre-charged to the power supply voltage or the reference potential, a potential distribution occurs in the bridge area and the level of the boosted power supply voltage VPP output from the boosting circuit is lowered.

Further, since the detector 18 detects the level of the boosted power supply voltage VPP to operate the oscillator 12, the boosting operation of the boosting circuit is continuously performed, and the current consumption is thus increased during the oscillation and boosting operations.

Accordingly, owing to unnecessary current consumption, yield is lowered.

Further, if a micro bridge occurs between the boosted power supply voltage VPP and another power supply voltage, it is difficult for the boosted power supply voltage VPP to arrive at the level intended. Thus, the voltage level of the word line is at less than the desired level when the first memory cell is accessed and the access operation cannot be performed smoothly.

Therefore, it is an object of the invention to address the problems outlined above.

Accordingly, the present invention provides a semiconductor memory device comprising: a peripheral circuit comprising a MOS transistor; a first boosting circuit for boosting a power supply voltage to provide a first boosted power supply voltage at a first level to a bulk bias terminal of the said transistor; and a second boosting circuit for boosting the power supply voltage to provide a second boosted voltage at a second level to the source terminal of the said transistor when an external input control signal is activated.

A further aspect of the invention provides a semiconductor memory device comprising: a first boosting circuit for boosting a power supply voltage to provide a first boosted power supply voltage at a first voltage level in response to the provision of the power supply voltage; a second boosting circuit for boosting the power supply voltage to provide a second boosted power supply voltage at a second level in response to an external control signal; and a peripheral circuit including a MOS transistor receiving the first and second boosted power supply voltages to a bulk bias and its source terminal respectively and adapted to output the second boosted power supply voltage to its drain terminal in response to a signal applied to its gate terminal.

The said MOS transistor may be a PMOS transistor, such as a PMOS transistor having an N-type well formed on a N-type well with P-type substrate.

The said external control signal may be a row address strobe signal.

The device may further comprise a control signal generator for providing a control signal boosted to the level of the power supply voltage to the second boosting circuit in response to the external control signal.

Preferably, the control signal generator includes a row address strobe input buffer for generating a clock in response to activation of the row address strobe signal and a row address enable signal activated a predetermined time after activation of the clock and a logic gate for combining the clock and the row address enable signal and to provide a voltage boosting control signal.

Preferably, the row address enable signal is continuously activated until a control signal is shut down, the control signal being used to control a word line and a control gate of a sense amplifier within the semiconductor memory device.

The said MOS transistor may form an inverter in the said peripheral circuit.

Preferably, the second boosted power supply voltage is at least as high as the first boosted voltage.

The above and other objects, advantages and features of the present invention will be more apparent from the following detailed description of a preferred embodiment taken with the attached drawings in which: Fig. 1 is a diagram illustrating a boosting circuit according to the prior art; Fig. 2 is an operating timing diagram of a boosting circuit shown in Fig. 1; Fig. 3 is a circuit diagram of a word line driver operated by a boosted power supply voltage output from a boosting circuit of Fig. 1; Fig. 4 is a diagram illustrating a boosting circuit implemented according to the present invention; Fig. 5 is an operating timing diagram of a boosting circuit shown in Fig. 4; and Fig. 6 is a diagram illustrating a word line driver operated by a boosting voltage output from a boosting circuit implemented according to the present invention.

Fig. 4 is a diagram illustrating a boosting circuit implemented according to the present invention, wherein the boosting circuit boosts the external power supply voltage Vs in response to the input state of an external control signal and outputs the boosted power supply voltage AVPP.

There are provided in Fig. 4 a booster 56, a transferrer 54, and a pre-charger 52. The booster 56 boosts the external power supply voltage to the boosted power supply voltage AVPP of a second voltage level, in response to the active state of a row address strobe signal RASB input from outside. The transferrer 54 transfers the voltage of an internal node PN2 boosted by the booster 56 to the level of the boosted power supply voltage AVPP. The pre-charger 52 pre-charges output nodes PN1 and PN2 of the booster 56 and a boosted output node, and stops the pre-charge operation in response to activation of the row address strobe RASB.

Fig. 5 is an operating timing diagram of a boosting circuit shown in Fig. 4. Referring to Fig. 5, the operation of Fig.

4 will now be explained.

As shown in Fig. 5, a clock PR and a row address enable signal PXAE output from a row address strobe input buffer (not shown) are all at the logic "low" level in a precharge interval where the row address strobe RASB used for accessing data of the memory cell is inactivated. The row address enable signal PXAE indicates that the row address is enabled when the row address enable signal PXAE is changed to the logic "high" level from the logic "low" level. On the other hand, when the row address enable signal PXAE is changed to the logic "low" from the logic "high" level, it indicates that the signal for controlling the word line and a control gate of the sense amplifier is inactivated. Thus, in the logic "high" level (VIH level interval) where the row address strobe RASB is inactivated, a NOR gate 50 receiving all of the clock PR and the signal PXAE provides a signal at the logic "high" level to the internal node N1 by means of the clock PR activated to the logic "high" level after a predetermined time goes by, in response to activation of the row address strobe RASB.

The signal of the internal node N1 at the logic "high" level is provided to input terminals of inverters 64 and 66 within the booster 56. The inverters 64 and 66 reverse the input signals to the logic "low" level, and then provide the signal at the logic "low" level to the nodes N2 and N3, respectively, which are connected to boost capacitors 68 and 70. The signal of the internal node N1 at the logic "high" level is applied to the gates of NMOS transistors 58 and 60 and the gate of an NMOS transistor 62, respectively, the NMOS transistors 58 and 60 each having a drain terminal and a source terminal connected between the power supply voltage Vcc and the first and second pre-charge nodes PN1 and PN2, and the NMOS transistor 62 having a drain terminal and a source terminal connected to the power supply voltage Vcc and the boosted output node. Therefore, the NMOS transistors 58, 60, and 62 are turned on when the row address strobe signal RASB is at the inactivated state (the logic "high" level) and pre-charge the first and second pre-charge nodes PN1 and PN2 and the boosted output node to the level of the "WcV" (here, the voltage "V*" is the threshold voltage of the NMOS transistors). The internal nodes N2 and N3 connected to one terminal of the boost capacitors 68 and 70 through the above operation, are precharged to the level of the ground voltage Vss Also, the first and second pre-charge nodes PN1 and PN2 and the boosted output node are pre-charged to the level of "Vcc- V n th - As shown in Fig. 5, in order to access the data of the memory cell, if the row address strobe RASB input from the outside is activated to the logic "low" level, the clock PR output from the row address strobe signal input buffer is changed to the logic "high" level. Thereafter, after a predetermined time goes by, the row address enable signal PXAE for enabling the row address buffer (not shown) is changed to the logic "high" level. Thus, the NOR gate 50 makes the level of the internal node N1 change to the logic "low" level, in response to the change of the clock PR to the logic "high" level. At this moment, all of the NMOS transistors 58, 60, and 62 whose gates are connected to the internal node N1 are turned off.

Moreover, the inverters 64 and 66 one terminal of which is connected to the internal node N1 reverse the signal of the logic "low" level output from the NOR gate 50, and then output the signal at the logic "high" level to the internal nodes N2 and N3, respectively. The signals of the internal nodes N2 and N3 at the logic "high" level are provided to one of terminals of the boost capacitors 68 and 70. The other terminals of the boost capacitors 68 and 70 are connected to the pre-charge nodes PN1 and PN2. Therefore, the boost capacitors 68 and 70 boost to the level of n 2Vcc- V" the voltage levels of the first and second pre-charge nodes PN1 and PN2 pre-charged to the level of "Vcc-V*" by the power supply voltage Vcc, as shown in Fig. 5. The voltage boosted to the level of "2VCc-V*" is provided to the gate and drain terminals of the NMOS transistor within the transferrer 54, so that the voltage level of the boosted output node is boosted to the level of 2(Vcc-V*) obtained by subtracting the threshold voltage of the transferrer 54 from the boosted voltage 2V,-V,.

Meanwhile, in order to complete the access of data from the memory cell, if the row address strobe signal RASB is changed to the logic "high" level, the clock PR output from the row address strobe signal input buffer (not shown) is changed to the logic "low" level. However, the row address enable signal PXAE output from the row address strobe signal input buffer is not changed to the logic "low" level at once, in response to the input of the row address strobe signal RASB at the logic "high" level. The reason is that the row address strobe signal PXAE is generally changed to the logic "low" level when the signal for controlling the word line and the control gate of the sense amplifier is shut down. Hence, the boosting circuit of Fig. 4 implemented according to the present invention continuously performs the boosting operation, and continuously outputs the boosted power supply voltage AVPP until the signal for controlling the word line and the control gate of the sense amplifier is shut down, even though the row address strobe signal RASB is changed to the logic "high" level from the logic "low" level. Then, if the control signal is shut down and the signal PXAE is thereby changed to the logic "low" level from the logic "high" level as shown in Fig. 5, the NOR gate 50 outputs the signal at the logic "high" level to the internal node N1. If the voltage level of the internal node N1 is changed to the logic "high" level, all the NMOS transistors 58, 60, and 62 within the pre-charger are turned on and the pre-charge operation is performed, thereby stopping the boosting operation.

As mentioned above, the boosting circuit implemented according to the present invention boosts and outputs the external power supply voltage Vcc as the boosted power supply voltage AVPP, in response to activation of the control signal applied from the outside, i.e., row address strobe signal RASB. Even though a detailed explanation is not provided above, it is possible to adjust the level of the boosted power supply voltage AVPP by regulating the threshold voltage of the NMOS transistors for charge or pre-charge of the boost capacitors. Thus, the level of the boosting circuit implemented according to the present invention is the same as, or higher than that of the boosted power supply voltage VPP output from the boosting circuit of Fig. 1.

The boosting circuit of the present invention constructed according to Fig. 4 can be used in effectively operating peripheral circuit of the semiconductor memory device, together with the boosting circuit according to the prior art. Prior to explaining Fig. 6, the boosting circuit having the configuration shown in Fig. 1 will be called a first boosting circuit and a boosting circuit having the configuration shown in Fig. 4 will be called a second boosting circuit.

Fig. 6 is a diagram illustrating a word line driver operated by a boosting voltage output from a boosting circuit implemented according to the present invention. In the configuration of the word line driver of Fig. 6, the same components are indicated by the same reference numbers.

Referring to Fig. 6, the boosted power supply voltage VPP output from the first boosting circuit is provided to the bulk bias terminals 44 of the first to third PMOS transistors 34, 38, and 40 constituting the word line driver, and the boosted power supply voltage AVPP output from the second boosting circuit is provided to the source terminals of the PMOS transistors 34, 38, and 40, respectively.

If the external power supply voltage Vcc is provided to the semiconductor memory device, the oscillator of the first boosting circuit is operated to generate the boosted power supply voltage VPP as discussed above. The boosted power supply voltage VPP output from the first boosting circuit is applied to the bulk bias terminals 44 of the first to third PMOS transistors 34, 38, and 40 of the word line driver, as shown in Fig. 6. In the meantime, the pre-charge voltage "Vcc-V*" output from the second boosting circuit is applied to the source terminals of the first to third PMOS transistors 34, 38, and 40 in the standby mode where the data of the memory cell is not accessed. In such a state, if the row address strobe signal RASB is activated, the second boosting circuit, as mentioned above, provides the boosted power supply voltage AVPP to the source terminals of the PMOS transistors 34, 38, and 40. Accordingly, the word line driver shown in Fig. 6 receives the boosted power supply voltage VPP and another boosted power supply voltage AVPP as operational voltages. And, under such a situation if a decoding signal is output from the row decoder 30, as discussed above, the decoding signal enables the word line WL to the level of the boosted power supply voltage AVPP.

Accordingly, when the semiconductor memory device is in the standby mode, only one line to be operated as a well bias of the PMOS transistors 34, 38, and 40 formed on an N-type well with P-type substrate, has the level of the boosted power supply voltage VPP among a plurality of potential nodes of the word line driver. Even if a bridge occurs between the source terminals of the PMOS transistors 34, 38, and 40 and another source terminal at a different level, since the level of the boosted power supply voltage VPP is lowered due to leakage current, the oscillation and boosting operations are not executed within the boosting circuit and the current consumption can be reduced during the standby mode to improve the yield in the semiconductor memory device. In addition, the boosting circuit of Fig. 6 provides the voltages to the source terminals of the PMOS transistors 34, 38, and 40 of the word line driver by operation of the second boosting circuit in the active cycle where the data of the memory cell is accessed. Thus, failure of the access operation can be prevented by boosting the voltage level of the word line of the memory cell which is initially accessed to the boosted power supply voltage VPP. Such a failure may result from a fall in the voltage level of the word line.

While only the word line driver has been described in the above embodiment of the present invention, various modifications can be implemented within the scope of the present invention. It will be apparent to one skilled in the art that the present invention can be applied to all circuits receiving the boosted power supply voltage VPP output from a conventional boosting circuit to the source terminal of the MOS transistor. Therefore, the present invention is not limited to only a word line driver.

As mentioned above, according to the present invention, the boosted power supply voltage AVPP higher than the external power supply voltage is provided to the bulk bias terminal of the PMOS transistor disposed within the peripheral circuit. Further, the boosted power supply voltage AVPP from the boosting circuit implemented according to the present invention is applied to the source terminal of the PMOS transistor. Thus, it is possible to prevent the reduction in yield due to leakage current during the standby mode of the semiconductor memory device, and also to prevent the failure in the access operation thereof.

Claims (12)

CLAIMS:

1. A semiconductor memory device comprising: a peripheral circuit comprising a MOS transistor; a first boosting circuit for boosting a power supply voltage to provide a first boosted power supply voltage at a first level to a bulk bias terminal of the said transistor; and a second boosting circuit for boosting the power supply voltage to provide a second boosted voltage at a second level to the source terminal of the said transistor when an external input control signal is activated.

2. A semiconductor memory device comprising: a first boosting circuit for boosting a power supply voltage to provide a first boosted power supply voltage at a first voltage level in response to the provision of the power supply voltage; a second boosting circuit for boosting the power supply voltage to provide a second boosted power supply voltage at a second level in response to an external control signal; and a peripheral circuit including a MOS transistor receiving the first and second boosted power supply voltages to a bulk bias and its source terminal respectively and adapted to output the second boosted power supply voltage to its drain terminal in response to a signal applied to its gate terminal.

3. A semiconductor memory device according to claim 1 or claim 2 in which the said MOS transistor is a PMOS transistor.

4. A semiconductor memory device according to claim 3 in which the PMOS transistor has an N-type well formed on a Ptype substrate.

5. A semiconductor memory device according to any one of claims 1-4 in which the said external control signal is a row address strobe signal.

6. A semiconductor memory device according to any one of claims 1-5, further comprising a control signal generator for providing a control signal boosted to the level of the power supply voltage to the second boosting circuit in response to the external control signal.

7. A semiconductor memory device according to claim 6 in which the control signal generator includes a row address strobe input buffer for generating a clock in response to activation of the row address strobe signal and a row address enable signal activated a predetermined time after activation of the clock and a logic gate for combining the clock and the row address enable signal and to provide a voltage boosting control signal.

8. A semiconductor memory device according to claim 7 in which the row address enable signal is continuously activated until a control signal is shut down, the control signal being used to control a word line and a control gate of a sense amplifier within the semiconductor memory device.

9. A semiconductor memory device according to any one of claims 1-8 in which the said MOS transistor forms an inverter in the said peripheral circuit.

10. A semiconductor memory device according to any one of claims 1-9 in which the said second boosting circuit is in accordance with any one of claims 12-18.

11. A semiconductor memory device according to any one of claims 1-10 in which the second boosted power supply voltage is at least as high as the first boosted voltage.

12. A semiconductor memory device substantially as described herein with reference to Figs. 4-6 of the accompanying drawings.